A parametric amplifier maybe used as a preamplifier, for example, in various transmission systems because of its capability of suppressing noise.
Such a parametric amplifier is generally of a lumped-constant diode type and requires another means, such as a circulator, for separation of input signals and idler signals. Further, since the amplifier is of a synchronizing type which requires complicated adjustment, it is difficult to design the amplifier to be variable in its amplification center frequency.
On the other hand, there has been proposed a travelling-wave parametric amplifier for the purpose of achieving a wider band amplification.
The basic system of the travelling-wave amplifier is to make a signal wave and a pumping wave concurrently travel through a non-linear medium to cause a parametric interaction therebetween, and to apply the energy of the pumping wave to both the signal wave and an idler wave which is newly generated, thus effecting signal amplification. To ensure this function, it is necessary to keep a constant phase correlation between the signal wave, the pumping wave and the idler wave; however, it is very difficult to satisfy this requirement.
This is generally caused by the phenomenom that the signal wave, pumping wave and idler wave travel at different speeds through the medium because their frequencies are different.